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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 4 |
| 3 | 32 |
| 4 | 320 |
| 5 | 3584 |
| 6 | 43008 |
| 7 | 540672 |
| 8 | 7028736 |
| 9 | 93716480 |
| 10 | 1274544128 |
| 11 | 17611882496 |
| 12 | 246566354944 |
| 13 | 3489862254592 |
| 14 | 49855175065600 |
| 15 | 717914520944640 |
| 16 | 10409760553697280 |
| 17 | 151860036312760320 |
| 18 | 2227280532587151360 |
| 19 | 32823081532863283200 |
| 20 | 485781606686376591360 |
| 21 | 7217326727911880785920 |
[0,1,4,32,320,3584,43008,540672,7028736,93716480, 1274544128,17611882496,246566354944,3489862254592, 49855175065600,717914520944640,10409760553697280, 151860036312760320,2227280532587151360, 32823081532863283200,485781606686376591360, 7217326727911880785920] |